The invention relates to data compression, and particularly to relocating compressed data tracks to and from storage devices.
Methods of sending compressed data from a disk subsystem to a host are well known in the prior art. Nevertheless, such methods are currently limited in that the compressed track is restored, i.e., written by the host, at the same storage location from which the track was read. While this may be acceptable for disk volume backup and restore, it is unacceptable for the backup and restore of application data sets that are backed up from one location and restored to another location.
More particularly, application data sets are seldom restored to the disk location from where they were originally backed up. By way of one example, data sets are sometimes deleted after backup and the corresponding disk space is used for another data set; and it can be undesirable to over-write the new data with restored data. By way of another example, utilities that compact volumes to make contiguous areas of free space move data sets around; and it can be undesirable to perform an additional backup simply because the data set was moved.
It is, accordingly, one object of the invention to provide methods for relocating compressed data tracks without the above-described problems. One specific object of the invention is to provide methods and systems for relocating compressed data tracks to and from Direct Access Storage Devices (xe2x80x9cDASDxe2x80x9d). A further object of the invention is to provide methods and systems to relocate compressed tracks, selectively, to compatible storage volumes. These and other objects will become apparent in the description that follows.
U.S. Pat. Nos. 5,615,329, 5,072,378 and 5,193,184 relate to storage systems, remote data duplex and/or virtual data storage, and provide useful background information for the invention. U.S. Pat. Nos. 5,615,329, 5,072,378 and 5,193,184 are thus herein incorporated by reference.
In one aspect, the systems and methods of the invention transfer compressed track images to the host with support information that provides for relocating the tracks from the source disk location to the new location, if desired, with a different track, a different cylinder, and/or a different disk in the format of the source track. In one specific aspect, data stored in compressed form is read by the host using a read protocol to read the compressed data; and that data is preceded by metadata that self-defines the track. The metadata solves the relocation problem of the prior art by creating a description of a compressed track that is invariant with its currently assigned location on a virtual volume. When the compressed track is written using a write protocol to write a compressed track, the metadata is used to restore the track in its newly assigned location on a different virtual volume, if desired.
In another aspect, when a compressed track is decompressed, a seed value in the metadata provides an identification tag for the data. This identification tag remains valid across relocation for data that is stored to a new location and subsequently decompressed.
In one aspect, the invention provides for relocating compressed tracks of different sizes so long as the new location has a compatible format and size with the original location at the time host-compressed track was read. This aspect is particularly useful in supporting IBM DASD systems such as model 3380-J and 3390-3, as these storage systems provide for different track sizes.
In certain aspects, the systems and methods of the invention also permit compression and alternatively decompression of data to and from the host, similar to storage systems in existence in the prior art. However, sending and receiving compressed data images from a storage volume with the host for purposes of backup and restore exemplifies one important advantage of the invention. Backup and restore data can then be moved quickly between the backup drive, e.g., a tape drive, and the storage volume. Further, with the invention, compressed data tracks from the backup device can be relocated to other locations in the virtual volumexe2x80x94also an advantage over the prior art.
In still another aspect, the invention provides a method for relocating data to a storage volume, including the steps of: storing a compressed track image of the data at a first location in a first storage volume; tagging metadata to the compressed track image; transmitting the compressed track image to a host; and storing the compressed track image at a second location in a second storage volume according to the metadata.
The method can also include the step of backing up the compressed track image in a storage device after transmitting the compressed track image to a host.
The method can further include the step of compressing the data prior to storing the compressed track image at the first location.
In other aspects, the first and second locations can be identical; and the first and second storage volumes can be the same.
In yet another aspect, the method includes decompressing the compressed track image and assigning a seed value to the metadata, so that the data remains identifiable across relocation.
In one aspect, the method includes the step of automatically modifying a count field of the compressed track image to match the second location.
In another aspect, the step of transmitting is preceded by the step of reading the compressed track image by a Read Protocol. The Read Protocol can include executing one or more of Define Extent, Locate Record and Read Track Commands.
In still another aspect, the step of storing includes the step of writing the compressed track by a Write Protocol. The Write Protocol can include executing one or more of Define Extent, Locate Record, Write, and Write Next Commands. In a preferred aspect, the step of writing by a Write Protocol includes the step of specifying the second location through a count field preceding the compressed track image.
In another aspect, the invention includes a system for backup and relocation of compressed track images. A host connects to a control unit, which stores the data as a compressed track image in a storage volume. The control unit responds to a read command from the host to transmit the compressed track image to the host; and the control unit assigns metadata to the image. The control unit responds to a read command from the host to restore the compressed track image into a location corresponding to the metadata. In restore, therefore, the compressed track is relocated, if desired.
In another aspect, the system includes a backup storage device to backup data from the storage volume.
In other aspects, the host includes read protocol logic to read the compressed track image from the control unit; and write protocol logic to restore the compressed track image to the storage volume.
The invention is next described further in connection with preferred embodiments, and it will become apparent that various additions, subtractions, and modifications can be made by those skilled in the art without departing from the scope of the invention.